The present invention relates to improvements in the field of spinal fusion to reduce the trauma and disturbance to surrounding tissues, reduce the time necessary to complete the operative procedure, increase the safety of the procedure, increase the accuracy of the procedure, provide improved instrumentation both for preparation and measurement, an improved procedure and an improved bone implant advantageously compatible with the instrumentation and procedure, both for anterior and anterolateral approaches to the spine with both open procedures as well as endoscopic procedures.
Fusion of part of the spine for instability, infection, tumor, degeneration and deformity has become a recognized surgical procedure for spine surgeons. The three approaches to the spine to perform these procedures are anterior, posterior and lateral, with the posterior being most common. It has become increasingly recognized that fusion between two adjacent vertebral bodies in the space occupied by the disc is desirable for biomechanical, neurophysiological and anatomical reasons. This xe2x80x9cinterbody fusionxe2x80x9d is biomechanically advantageous because the area to be fused is subjected to compressive loads rather than tensile forces as in the case for posterior element fusions. It also offers the best way to restore or maintain the opening of the neuroforamina and to restore or maintain lumbar lordosis. Quite often spinal deformity correction cannot adequately be performed without interbody surgery.
Lumbar interbody fusion is usually performed from either the anterior or posterior approaches although lateral approaches are occasionally used as well. The goals of interbody fusion are as follows: I. To maintain sagittal and frontal plane alignment of the spine, 2. To maintain or restore intervertebral space dimension, 3. To achieve a solid fusion. To this end a number of surgical techniques and graft materials have been utilized to attain a safe and successful pain relieving fusion.
Reduced to the most rudimentary level, anterior interbody fusion is performed by removing all or part of the intervertebral disc, preparing the bony interspace and placing graft material into the space. Supplemental fixation devices are often used to keep the graft from xe2x80x9cbacking out,xe2x80x9d getting crushed by the compressive and complex loads and to help maintain alignment while the fusion takes place. In prior years various bone graft materials utilized have been bovine zenograft; allograft tibia, fibula, femur, iliac crest and autograft iliac crest, and fibula. Success rates in terms of achieving fusion varied from 63-95%. They all shared the problems of graft failure from dislodgement, fragmentation, failure to achieve fusion or loss of alignment from subsidence.
More recently threaded cylindrical xe2x80x9ccagesxe2x80x9d made from either titanium or fresh frozen allograft femoral diaphysis have been used. The stability provided by the threaded design allowed these implants to be used as a xe2x80x9cstand alonexe2x80x9d device not requiring further accessory stabilization. However, there have been increasing reports of non-union when initially fusion was thought to have occurred and subsidence with sinking of the implants into the vertebral body.
Threaded cylindrical cages require tapping to insert the cage. Tapping causes destruction of the supportive end plates of the vertebra allowing subsidence or xe2x80x9csinking inxe2x80x9d of the implant into the body of the vertebra. This causes a loss of height of the spinal column with narrowing of the foramina and potentially compression of the exiting nerve root. There is also a flattening of the lumbar lordosis resulting in lower back pain. Furthermore the long term effects on the body from the entrapped metal implant and its local effects on the spine are unknown. If removal becomes necessary due to pain or infection the metallic cages are virtually impossible to remove without endangering the greater vessels overlying the anterior spine and necessitating massive destruction of the involved vertebrae. This creates an almost impossible situation to restabilize the spine. Consequently there is increasing awareness that a better design and conceived bone or non metallic biomaterials implant interbody fusion technique is necessary.
In this surgical procedure as it generally and currently is practiced, the body is entered and the spine is accessed from its anterior or lateral side. Layers of tissue surrounding the spine have to be opened carefully so that adjacent nerves and blood vessel structures, including the aorta and inferior vena cava are not ruptured and preferably are not immobilized more than necessary. Once the spine is accessed, the intervertebral disc between two adjacent vertebra must be carefully and safely removed.
A common implant used in intervertebral fusion is a femoral diaphyseal ring both freeze dried and fresh frozen allograft. This is used both for structural support to maintain the intervertebral space and to promote bone growth to fuse two adjacent vertebra together. A serious problem exists with respect to the surgical procedure of accessing, preparing the space between adjacent vertebrae, and in inserting and positioning the femoral ring allograft. One company""s answer is a triple jointed spreading device. A pair of spreading levers, referred to as distractor blades, are laterally offset mounted from the centerline of the last joint of the triple jointed spreading device. The spreading levers are thin, and relatively narrow and thus potentially and actually unstable increasing the danger of inadvertent injury of surrounding tissues. The spreading device is bulky, long and since it extends straight into the space between the two vertebra, it blocks the approach and takes up valuable space and blocks needed vision into the critical operative area. The offset is for the purpose of inserting a second set of pliers-action implant holder to just clear the offset.
Unfortunately, the pliers-action implant holder must push the implant into a space which has a height taken up by the thickness of the distractor blades. This poses the danger again of dislodging the spreader device potentially causing tissue and vascular injury. Aside from the inherent instability of having spreaders, the use of the triple jointed spreading device requires excessive spreading in order to achieve its goal of providing working room to shape the interspace. Overspreading of the interspace can damage, even fracture, the vertebra. It also potentially damages the discs above and below the working level and can cause neurological injury with foraminal compression.
In some cases, a spacing tool is used or inserted while the intervertebral space is distracted with the three joint distractor. The spacing tool conventionally used is a rectangular paddle mounted at the end of a straight handle. The spacing tool is cumbersome because the handle which extends straight from the operational area further gets in the way of the surgeon. Insertion of the spacing tool is also cumbersome as it can be inserted only if the size of the inter vertebral opening exceeds the clearance size of the width of the rectangular paddle. Because the natural disc space is biconcave, the surgeon is faced with the problem of fitting a rectangular profile object into an elliptical space. This results in poor contact between the end plates of the adjacent vertebra and the surface of the bone graft which militates against successful fusion.
If the surgeon chooses to carve a rectangular space to accommodate the spacer or the graft, he must necessarily remove a great deal of the all important end plate thereby weakening the most structurally supportive part of the vertebra. This then subject the fusion site to subside and thereby resulting in unwelcome deformity with loss of normal spinal curvature and foraminal narrowing. The operation should involve only enough access to accomplish the objective of safely preparing the interspace and inserting a graft. Aspects of attaining this objective includes elimination of excessive spreading of adjacent vertebrae, enabling the surgeon to operate with as full an amount of control over the surgical field as is possible, as full an amount of vision into the surgical field as is possible, reduction of obstructions into the surgical field, and importantly, supplying the surgeon with tools which enable complete force control and selection. Proper surgical tools should lend themselves for automatic adaptation for patients of different size and of different complications. The excess force and over spacing should be eliminated.
The shape, stability, handling and force used in preparation and insertion of the implant is also a problem with spine fusion surgery. Where the implant is to be inserted, and particularly where the adjacent vertebrae are under compressive force, it may be expelled from the intervertebral space as the result of such compressive forces. The insertion using a poor grasping tool typically allows rotation or lateral displacement of the graft before the surgeon has a chance to make final placement and secure it.
The degree of spreading of two adjacent vertebrae away from the intervertebral space should be limited to avoid trauma to surrounding areas, yet enable the surgeon to access the area for removal of the disc and shaping of the interspace. Current surgical instruments available for this purpose do not enable both access, full disc removability and interspace shaping without obstructing the surgical field or unduly lengthening the time required for the procedure.
Currently used instruments to prepare the interspace such as osteotomes, chisels, curettes, rongeurs and high speed drills all have some application as well as drawbacks. The use of any combination of these instruments still does not achieve the goal of a safe, quick and anatomically shaped interspace to match a like contoured implant. Extensive use of curettes is time consuming and leaves an uneven end plate surface. Osteotomes and chisels are often too short for safe application and will not result in the ability to perform precision work. High speed drills can be quick, but can easily wrap up adjacent soft tissue resulting in catastrophic vascular injury. It is also difficult to control in the more posterior recesses of the interspace and can transgress the posterior rim and inadvertently enter the spinal canal and cause permanent neurological injury.
Another feature lacking in surgical instruments is the ability to remove instruments in a way which will not encourage side to side loosening. When an inserted instrument becomes jammed, lateral movement or force will tend to damage the surrounding areas. The surgeon""s lack of control over exit angle as well as entry angle is a problem in performing this type of procedure. This is especially complicated by the fact that major blood vessels lie to either side of the operative area.
The obstruction of the surgical field is another problem. Extremely long, complicated instruments, especially those instruments which have hand engagement members located far from the surgical field, cause a significant obstruction problem. This is compounded by instrumentation which is used to hold the adjacent vertebrae apart. At the point in the procedure where the implant is to be implanted or implaced, a large number of instruments, particularly long, obstructing instruments, may be simultaneously present. The resulting obstruction is both significant and hazardous.
Implants, such as femoral diaphyseal rings currently used give the surgeon problems of (1) rotating in the interspace during insertion, (2) not remaining positioned properly to the surgical instrument utilized for implantation and fixation, (3) backing out of the interspace, (4) fracturing during insertion and (5) failure to achieve fusion.
Ideally, the implant would be contoured to restore the lumbar lordosis and match the shape of the anatomical interspace. It should have desired surface etching to securely mate to an entry instrument and resist extrusion and rotational shear forces. It should also have a surface design to increase the surface area in order to promote more rapid bone growth. No design has yet provided a solution to these problems in the allograft diaphyseal ring implant field.
What is therefore needed is a set of surgical instruments which can be utilized for spine fusion operations which reduce the visual and manual obstruction in the surgical field, give the surgeon more options for manipulation, better secure the implant on insertion and fixation, better orient the implant, enable a lesser magnitude of force to be applied to the procedure, and which enables the procedure to proceed in less time, more safely, and with better surgical control.
Other needs include anything which will reduce time during the operation, especially time spent in (1) removal of cartilage material, (2) shaping the intervertebral disc space to accept the implant, (3) selecting the correct sized implant for insertion to thus eliminate as far as possible having to remove the implant and increasing the possibility that it may be damaged from removal, or repeated re-insertions, and (4) further shaping the implant while the patient is in the midst of the operation extends the danger to the patient, the cost of operating theater time, creating the probability even in the hands of skilled surgeon that the implant may be over adjusted or improperly adjusted followed by improper implantation because no other implant was available or by wasting of a valuable implant. Not included in the list above are probabilities of having to re-set up for cartilage removal, as well as having to set up again for re-doing any porion of the operative procedure. A needed system should insure a proper fit, eliminate wasted time, and place the surgeon in a position to exert better management over the operative procedure.
The system and method of the invention includes surgical instrumentation which enables the spine fusion procedure to proceed more accurately, efficiently and safely by offering a surgical procedure for the anterior (and anterolateral) interbody approach along with new and safer instruments and custom designed implants, which allow precision placement of the graft under proper tension and in the best position to achieve spine balance and fusion. In the order in which they are used, improvements in a distractor, box chisel, curette, femoral ring implant and bone graft holder impactor will be illustrated.
A distractor includes a detachable hollow oval shaped handle and utilizing an exterior ring lock for selective engagement while providing acceptance of impact energy from the handle. The tip of the distractor is shaped for use on the flat side where necessary, but generally for use by insertion into the inter vertebral space utilizing its second greatest dimension on a gentle taper to spread adjacent vertebra. Since the spreading of the vertebra occurs primarily at the anterior side, and since spreading occurs based upon entry of the distractor, the adjacent vertebra are not over spread in order to support a shorter dimensioned spreader tool. Further, since the outer periphery of adjacent vertebra include a lip structure forming the narrowest part of the entry space, the insertion of the distender of the invention provides the least invasive method of setting the intervertebral open space, since for a given amount of spreading the distractor enters the inter vertebral space to a lesser degree than would be the case with other distraction tools. Variations include a roughening of the edge of the distractor which can wear away a slight notch in the bone to accomplish at least two objectives. The formation of a notch is advantageous because it stabilizes the resting location of the distractor, and creates fine bone fragments in the space between the vertebrae to help accelerate the fusive bone growth. More importantly, when the notches are formed upon insertion of the distractor, the distractor is stabilized both from the presence of the notches, as well as from the natural frictional fixation of the roughened edges of the distractor. The blunt end of the distractor replaces the relatively thinner, sharper end of pliers-type distractors. Preferably two sizes of distractor described herein should be included within the surgeon""s available instrument set.
An advantageous box chisel is disclosed having a curved upper and lower blade which are both beveled in an direction disposed toward the centerline of the box chisel. The box chisel shape more nearly matches the intervertebral space. An open portion of the box chisel in the rear direction enables the surgeon to see whether and how much material to be removed has collected in the box chisel to enable it to be emptied. The box chisel, and other instrumentation includes a scale to give the surgeon an instant reading on the depth of penetration into the intervertebral space.
A curette is disclosed which had advantageous angling of the end portion to better enable the material in the intervertebral space to be removed.
An intervertebral space shaped rasp is provided for completing the cartilage removal process. The intervertebral rasp is available to the surgeon in a variety of sizes which enables the surgeon to either (1) quickly select the needed tool, or (2) utilize a series of such rasp tools to sequentially remove cartilage material. In either the anterior or the anterolateral procedure, the rasping action naturally occurs with a slight pivoting side to side motion of the handle about an axis through the intervertebral space. The rasp surfaces both above and below generally extend across the face of the rasp such that a pivot action about a main axis of the rasp will produce a relatively even material removal action, especially radially. The shape of the rasp not only matches generally the intervertebral space, but is shaped so as to bear slightly more axial pressure at the center of the interaxial space and slightly less at the radial outermost areas in order to take advantage of the differentially lesser rasping motion at the center. Thus for a given angle of displacement, equal material should be removed from the center and the periphery of the rasp surface. The result will be an even removal of material which will even further match the bone implants which are preferably pre-formed to a variety of sizes, but of a uniform shape within each size range.
A series of measuring gauge instruments are provided to enable the cleared intervertebral space to be probed to ascertain the correct size of implant to be utilized. Given the fact that the intervertebral space is curved and will give a different measurement depending upon where the vertical distance is measured, the introduction of a matched set of both rasps and sizers which correspond to a matched set of implants goes a long way toward both standardization of the procedure as well as creating increased safety, certainty and consistency in the vertebral implant operative procedure.
Further, the implant of the invention is pre-formed with a series of beneficial shape and structure attributes. All of the implants encompassed in the invention can be of any material ranging from human harvested allograft to modern manufactured materials. The modern manufactured materials can be of any construction and from any materials, but especially from materials having surface openings from about fifty to five hundred microns in average diameter, and a depth of from about one half to about three millimeters. The depth and opening size, stated here as an average diameter for convenience only, are for the purposes of promoting rapid, secure fusion.
In terms of its contribution to the operative system, including instrumentation as a whole, the implant is formed in sizes which preferably correspond to the gauges to facilitate quick, easy and definite selection.
Several embodiments of bone implants are disclosed including annular flat surface implants having angled surfaces, implants having line slots to help in the insertion and orientation on insertion and in registering the implant with an impactor. Where the implant is a human harvested allograft, it will have a central aperture, into which may be introduced an absorbent substrate, such as a collagen sponge, saturated with bone morphogenetic protein substance to promote even more rapid fixating bone growth. In addition, autogenous bone can be introduced, typically harvested from the iliac crest of a patient undergoing the implant procedure. Although the human harvested allograft is supplied with the a single pre-existing bore or aperture, a manufactured implant can either (1) have a series of bores into which the bone morphogenetic protein or autogenous bone can be introduced to facilitate growth, (2) have other facilitating structure into which the bone morphogenetic protein or autogenous bone can be introduced, or (3) be manufactured as an integrated structure with the into which the bone morphogenetic protein or other substance can be pre-set for timed release or for invasive displacement from the implant structure. All of the implants discussed below are considered to have these possibilities and more as technology advances.
Anterolateral implants are specially designed with surface effects which facilitate the anterolateral approach, which may typically occur at angles from about 20xc2x0 to about 70xc2x0 away from a straight anterior approach.
A first embodiment of an impactor includes a pair of jaws which fit loosely in an impact frame and which are held in place using a thumb adjust nut. The impact frame applies impact energy directly to the implant independently of the grasping jaws. A second embodiment of an impactor includes a pair of hinged jaws which are urged together upon withdrawal into a sleeve and which direct impact energy through the combination of an impact head of a draw bolt into a main body of the hinged jaws, along with some impact energy through the sleeve. Turning of the impact head causes the jaws to move forward in the sleeve and enables the jaws to move apart to release the implant.